The present invention is directed to an end-of-service indicator including a porous waveguide, preferably an optical fibre, for the detection of the saturation of a respirator cartridge.
Respirator cartridges, and devices which incorporate them, are among the most important security devices used to protect the health of workers. More than 10 million respirator cartridges are used each day in North America.
One of the critical elements related to efficient and safe use of these cartridges is their life span. In the case of gas and vapour pollutants, often the only indicator of the saturation of the cartridge is the odor of the pollutant. This is a dangerous indicator of the end of service of the cartridge since there are many pollutants whose olfactory detection level is below the Threshold Limit Value (TLV). For a user, it is desirable that the cartridge includes an active indicator to indicate without ambiguity that the useful life of the cartridge has ended. In 1984, the National Institute for Occupational Safety and Health (NIOSH) published standards for the certification of active end-of-life indicators to encourage the development of such systems.
One type of active end-of-life indicator presently under investigation is based on the use of polymer films containing carbon particles. The presence of soluble organic vapours causes a change in the resistance of the film and it is this element that is measured. Another type of indicator is described in U.S. Pat. No. 4,146,887 to Magnante, describing the use of a temperature sensor (thermocouple or other) to detect the exothermic reaction of gas/vapour absorption in a respirator cartridge.
A related field to the invention is the field of fiber optic chemical sensor (FOCS). Many articles have been published and several patents awarded for the use of FOCS to detect solvent or chemical products. The vast majority of FOCS use a spectroscopic approach in one form or another, i.e. they rely on light absorption at specific wavelengths to identify chemical species.
Some FOCS measure light loss caused by refractive index change. For instance, U.S. Pat. No. 5,828,798 (HOPENFELD JORAM) describes the use of a specially shaped plastic fiber with a coating that dissolves in the presence of the analyte to be detected. The HOPENFELD patent claims a fiber optic sensor different from other fiber optic sensors in that the cladding material has a refractive index superior to the refractive index of the core, and that the fiber has a specific shape to increase its sensitivity. Furthermore, in the HOPENFELD patent, the cladding is chosen to be specific to a particular analyte and will dissolve in the presence of the analyte. As a result, the light transmitted by the fiber increases in the presence of the analyte.
Few FOCS use porous material, although an article published in Electronic Letters, vol. 24, p. 42 (1988) describes the use of an optical fibre having a porous cladding to measure humidity levels. In this case, the optical fibre is manufactured by depositing porous glass soot on a pure silica fibre. The intensity of the transmitted light decreases by 60% when the relative humidity reaches 90%. In this case, the fibre is straight.
U.S. Pat. No. 5,250,095 (SIGEL JR GEORGE ET AL) describes the use of a porous fiber as a chemical sensor. In this case, the pores are used as an optical chamber to contain the agent which will cause a change in the optical transmission of light by the agent and not because of changes to the guiding properties of the fiber. The SIGEL patent is very similar to standard spectroscopy techniques to detect and identify substances: it uses a tunable narrow-wavelength light source (lamp+monochromator), an optical cell (the porous fiber) and a detector to measure the change in absorption of light as a function of wavelength. The agent(s) of interest for sensing are optically detected.
The following U.S. patents are also of interest:
U.S. Pat. No. 4,154,586 Jones et al. RESPIRATOR CARTRIDGE END-OF-SERVICE LIFT INDICATOR SYSTEM AND METHOD OF MAKING;
U.S. Pat. No. 4,530,706 Jones RESPIRATOR CARTRIDGE END-OF-SERVICE LIFE INDICATOR;
U.S. Pat. No. 4,699,511 Seaver REFRACTION SENSOR;
U.S. Pat. No. 4,834,496 Blyler, Jr. et al. OPTICAL FIBER SENSORS FOR CHEMICAL DETECTION;
U.S. Pat. No. 4,846,548 Klainer FIBER OPTIC WHICH IS AN INHERENT CHEMICAL SENSOR;
U.S. Pat. No. 5,280,548 Atwater et al. EMISSION BASED FIBER OPTIC SENSORS FOR PH AND CARBON DIOXIDE ANALYSIS;
U.S. Pat. No. 5,512,882 Stetter et al. CHEMICAL SENSING APPARATUS AND METHODS;
H1470 Ewing et al. REFRACTIVE INDEX-BASED SENSOR FOR THE DISCRIMINATION OF CHLORINATED HYDRO-CARBONS FROM GROUNDWATER.
It is an object of the present invention to provide a respirator cartridge having a waveguide end-of-service indicator that is universal, active, unambiguous and simple in its construction. In accordance with the invention, this object is achieved a respirator cartridge having a waveguide end-of-service indicator, the end-of-service indicator comprising a waveguide having two extremities, one of the extremities being connected to a light source, the other of the extremities being connected to a detector which measures the intensity of light transmitted by the waveguide. An alarm is operatively connected to the detector and is triggered when the intensity of light measured by the detector is below a predetermined level. The end-of-service indicator is characterised in that at least a portion of the waveguide is porous. In use, when the end-of-service indicator is placed inside or at the exit of a respirator cartridge having a gas/vapour sorbent, and the respirator cartridge is used in a toxic environment, the gas/vapour sorbent gradually becomes saturated as does the porous waveguide, thereby lowering the guiding and transmission properties of the waveguide and triggering the alarm. In a preferred embodiment, the waveguide is an optical fibre.